Elastic Member Clamps

ABSTRACT

The present application generally relates to orthopedic stabilization systems, and in particular, to systems including clamps. The clamps can be used in addition to or to replace hooks that grasp onto bone members, such as the lamina. One example of such a clamp is an in-line clamp that includes a central opening for receiving a rod member, a first opening for receiving a set screw and a second opening for receiving an elastic member therethrough. Another example of such a clamp is an off-set clamp that includes an upper plate, a bottom plate, and an opening for receiving a rod therein. The upper plate can be separated from the bottom plate to make space for an elastic member that can be secured within the plates. Tulip clamps that utilize one or more elastic members are also provided.

FIELD OF THE INVENTION

The present application is generally directed to orthopedicstabilization systems, and in particular, to systems including clampsand rod members.

BACKGROUND

Many types of spinal irregularities cause pain, limit range of motion,or injure the nervous system within the spinal column. Theseirregularities can result from, without limitations, trauma, tumor, discdegeneration, and disease. Often, these irregularities are treated byimmobilizing a portion of the spine. This treatment typically involvesaffixing a plurality of screws, hooks and/or clamps to one or morevertebrae and connecting the screws, hooks and/or clamps to an elongaterod that stabilizes members of the spine.

Accordingly, there is a need for improved systems involving screws,hooks and/or clamps for spinal stabilization.

SUMMARY OF THE INVENTION

Various systems, devices and methods related to spinal clamps areprovided. In some embodiments, a spinal system comprises a clamp forreceiving an elongate rod therein, wherein the clamp comprises an inneropening for receiving the elongate rod, a first opening in communicationwith the inner opening, and a second opening in communication with theinner opening; a set screw received in the first opening of the clamp; abushing positioned at a distal end of the set screw; and an elasticmember received in the second opening of the clamp, wherein the elasticmember is configured to be in contact with the elongate rod received inthe clamp.

In other embodiments, a spinal system comprises a clamp for receiving anelongate rod therein, wherein the clamp comprises an inner opening forreceiving the elongate rod, a first opening in communication with theinner opening, and a second opening in communication with the inneropening, wherein the inner opening includes a groove for receiving anelastic member therein; a set screw received in the first opening of theclamp; and an elastic member received in the second opening of theclamp, wherein the elastic member is configured to be in contact withthe elongate rod received in the clamp.

In other embodiments, a spinal system comprises a clamp for receiving anelongate rod therein, wherein the clamp comprises an inner opening forreceiving the elongate rod, a first opening in communication with theinner opening, and a second opening in communication with the inneropening; a set screw received in the first opening of the clamp; abushing in contact with a distal end of the set screw, wherein the setscrew includes a protrusion that extends past a portion of the bushing;and an elastic member received in the second opening of the clamp,wherein the elastic member is configured to be in contact with theelongate rod received in the clamp.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top perspective view of an in-line clamp according to someembodiments.

FIG. 1B is a side cross-sectional view of the in-line clamp in FIG. 1A.

FIG. 2A is a side cross-sectional view of an alternative in-line clampaccording to some embodiments.

FIG. 2B is a top perspective view of the in-line clamp in FIG. 2A.

FIG. 2C is a side cross-sectional view of the in-line clamp in FIG. 2A.

FIG. 3A is a side cross-sectional view of an alternative in-line clampaccording to some embodiments.

FIG. 3B is a top perspective view of the clamp in FIG. 3A.

FIG. 4A is a top perspective view of an off-set clamp according to someembodiments.

FIG. 4B is a cross-sectional view of the off-set clamp in FIG. 4A.

FIG. 4C is a top perspective view of the off-set clamp in FIG. 4A withan elastic member.

FIG. 4D is a cross-sectional view of the off-set clamp in FIG. 4A withan elastic member.

FIG. 5A is a top perspective view of a tulip clamp according to someembodiments.

FIG. 5B is a side cross-sectional view of the tulip clamp in FIG. 5A.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present disclosure relates to spinal stabilization devices, and inparticular, clamps that utilize elastic members to grasp onto bone. Thevarious clamps can be placed in many positions relative to a bonemember, such as in-line or off-set.

Many spinal components exist to assist in stabilizing spinal members.Among the components that are used are spinal hooks, which can grasponto bone. While spinal hooks are effective and can be less disruptiveand prone to causing injury compared to other components, such asscrews, there is a possibility of the hooks disengaging post surgery,therefore leading to potentially additional surgical intervention torectify.

The present application is directed to spinal stabilization devices thatovercome challenges associated with current spinal devices. Inparticular, it has been found that spinal clamps can be effectivelyprovided that use elastic members, such as elastic bands, to grasp ontobone members. The use of the elastic members advantageously secures theclamps to bone, and reduces the risk of the devices being inadvertentlyremoved from the bone post-surgery.

FIGS. 1A-1C illustrate different views of an in-line clamp utilizing anelastic member, according to some embodiments. The in-line clamp 10comprises a body 12 for receiving a rod member 80 therein. The in-lineclamp 10 is configured to receive an elastic member 60 therethrough tosecure the clamp 10 to a bone member (e.g., a vertebral body).

The in-line clamp 10 includes a body 12 that forms a curved opening ormouth 17 for receiving a rod member 80 therein. As shown in FIG. 1A, insome embodiments, the curved opening 17 of the body 12 is formed facingdownwardly over the rod member 80, such that the rod member 80 isbottom-loaded relative to the clamp 10. Advantageously, the curvedopening 17 is also configured to receive a portion of the elastic member60, which wraps around a vertebral body or bone member. As shown in FIG.1A, the elastic member 60 can be positioned such that a first portion ofthe elastic member 60 is in contact with a first side of the rod member80 and a second portion of the elastic member 60 is in contact with asecond side of the rod member 80 opposite from the first side afterlooping the elastic member around a bone member. In other embodiments,such as shown in FIG. 2A, the elastic member 60 can be configured suchthat portions of the elastic member 60 remain pressed between one-sideof the rod member 80 and an inner wall of the clamp 10, even afterlooping the elastic member 60 around a bone member. One skilled in theart will appreciate that the positioning of the elastic member 60relative to the rod member 80 and the clamp 10 can vary, and that theillustrations shown herein are not meant to limit the positionsavailable for placing the elastic member, but rather show options forplacing the elastic member in the system.

The curved opening 17 for receiving the rod member 80 is formed by innerwalls of the clamp 10. In some embodiments, the curved opening 17 has aradius that can accommodate both the rod 80 and the elongate member 60placed therein. As shown in FIG. 1B, the inner walls of the clamp 10 caninclude a track or groove 32 formed therein that runs along the innerwalls of the clamp 10. The groove 32 advantageously accommodates theelastic member 32 therein. In some embodiments, the groove 32 has awidth that is approximately the same as the width of an elastic member60 positioned therein. With the addition of the groove 32, the clamp 10,rod member 80 and elastic member 60 can be held together, even beforetightening the set screw 25 (as discussed below). In some embodiments,the groove 32 runs substantially or completely along the inner walls ofthe clamp 10.

The curved opening 17 is in communication with a first opening 14 and asecond opening 16, each of which extends through the body 12 of theclamp 10. The first opening 14, which runs diagonally relative to avertical mid-plane of the device, is configured to receive a threadedset screw 25 therein. When the rod member 80 and elastic member 60 havebeen placed in a desired position within the mouth of the clamp 10, theset screw 25 can be downwardly threaded to apply a compression force onthe rod member 80 and elastic member 60 to securely capture the memberswithin the clamp 10.

In some embodiments, a separate bushing 28 can be attached to a distalend of the set screw 25, as shown in FIGS. 1A and 1B. The bushing 28advantageously provides an intermediary contact surface between the setscrew 25 and the elastic member 60, thereby preventing the elasticmember 60 from fraying or tearing from the contacting the surface of theset screw 25. As shown in FIG. 1B, the bushing 28 has a curved contactsurface 29 that conforms to the shape of the rod member 80 and elasticmember 60 positioned in the mouth of the clamp. The curved contactsurface 29 advantageously serves as a pressure distribution surface thatcomfortably distributes pressure around the rod and elastic member 60 asthe threaded set screw 25 is downwardly threaded. In other embodiments,the contact surface 29 of the bushing 28 is partially straight. Whilethe set screw 25 and bushing 28 are illustrated as separate components,in other embodiments, the two components are integrated components. Theset screw 25 and bushing 28 can be molded together, or can be formed ofa monolithic member. In some embodiments, the set screw 25 and thebushing 28 are formed of different materials, while in otherembodiments, the set screw 25 and the bushing 28 are formed of the samematerials. In some embodiments, the set screw 25 and/or bushing 28 canbe formed of different biocompatible metals, such as stainless steel,titanium or cobalt-chrome.

The second opening 16, which runs generally through a vertical mid-planeof the device, is configured to receive one or more elastic members 60therethrough. As shown in FIG. 1A, this central opening 16 is wideenough to receive two ends or portions of an elastic member 60 that hasbeen looped around a vertebral body. One skilled in the art willappreciate that the positioning of the first and second openings 14 and16 should not be limited. For example, in alternative embodiments, thepositions of the first opening 14 and the second opening 16 can beswitched. Alternatively, in other embodiments, the second opening 16 forreceiving the ends of the elastic members 60 can be moved away from thevertical mid-plane of the device.

In some embodiments, the elastic member 60 can be a cable. Preferably,the elastic member 60 is a wide elastic band 60. The use of a wideelastic band 60 can advantageously reduce the risk of damage to tissuelacerations or injury. In some embodiments, the elastic band 60 isbetween 2 and 8 mm, or greater than 4 mm. In some embodiments, the bandis composed of a polymer, such as PET. To ensure that the clamp 10remains secured to a bone member via the elastic band 60, a tensionercan be included as part of the system to make sure that the bands are inproper tension and tightness.

The in-line clamp 10 can be used as follows. In some embodiments, theelastic member 60 (e.g., band) can first be introduced to the clamp 10without the rod 80 inserted therein. The elastic member 60 can bepositioned along and within the single groove 32 that extends along aninner surface of the clamp, which advantageously helps to center theelastic member 60. Both ends of the elastic member 60 can extend throughthe second hole 16, thereby forming a loop at the bottom of the elasticmember 60. The loop of the elastic member 60 can be wrapped around aportion of a spine (not shown), such as a lamina. With the elasticmember 60 in place, a rod member 80 can be received through the bottomopening 17 of the clamp 10. Once the rod member 80 is pushed through thebottom opening 17 of the clamp 10 and against the inner walls of theclamp, the rod member 80 is provisionally held in the clamp 10. At thistime, the rod member 80 is advantageously free to translate along thedirection of its longitudinal axis.

With the rod member 80 in the clamp, a tensioner can be used to tensionthe elastic member 60, thereby pulling the spine to the rod member 80 inorder to correct a deformity. When adequate correction is obtained, theset screw 25 can be downwardly threaded to tighten and securely capturethe elastic member 60 and rod member 80. The bushing 28, which serves aseither a floating piece that is separate from the set screw 25 or anintegrally formed piece with the set screw 25, is positioned at thedistal end of the set screw 25 to distribute the tightening load of theset screw 25 uniformly across the elastic member 60 and the rod member80. As the set screw 25 is downwardly threaded, the set screw 25compresses against the elastic member 60 and rod member 80, therebysecuring the system. At this time, the rod member 80 is locked in placeand is no longer free to translate.

FIGS. 2A-2C illustrate different views of an alternate in-line clamp 10according to some embodiments. The in-line clamp 10 in these figuresdiffers from the clamp in FIGS. 1A and 1B in that it has a first opening14, a second opening 16 and an additional third opening 18 that extendsthrough the body of the clamp. As shown best in FIG. 2A, the additionalthird opening 18 is configured to receive two portions or strands of alooped elastic member 60, which also extend into the second opening 16.In addition, while the curved opening 17 opens downward such that therod member 80 remains bottom-loaded, the curved opening 17 is now morediametrically positioned relative to a vertical mid-plane of the device.

In this embodiment, the elastic member 60 passes through both the secondopening 16 and the third opening 18. A loop is formed by the elasticmember 60 closer to the third opening 18 and is capable of wrappingaround a bone member. In the present embodiments, when a rod member 80is positioned in the curved opening 17 of the clamp 10, the elasticmember 60 is kept on one side of the rod member 80. In other words, theelastic member 60 is positioned between the rod member 80 and the innerwalls of the clamp 10, as shown in FIG. 2A. The addition of the thirdopening 18 thus provides additional ways to accommodate the elasticmember 60 relative to the rod member 80 and the clamp 10.

FIGS. 3A and 3B illustrate different views of an alternative in-lineclamp 10 according to some embodiments. The in-line clamp 10 in thesefigures differs from the clamp in FIGS. 1A and 1B in that it has a firstopening 14, a second opening 16, additional third and fourth openings18, 19, and a unique set screw 25 having an extension member 26. Boththe third opening 18 and the fourth opening 19 are in communication withthe opening 17 for receiving a rod member, and are positioned near alower portion of the clamp 10.

The clamp 10 is configured to receive an elastic member 60 therethrough.In some embodiments, a first end of the elastic member 60 can extendthrough the third opening 18 while a second end of the elastic member 60can extend through the fourth opening 19, such that both the first andsecond ends of the elastic member 60 meet and pass through the secondopening 16. A loop is formed at the bottom of the elastic member 60 toreceive a bone member. In alternate embodiments, a first end of theelastic member 60 and a second end of the elastic member 60 can passthrough the third opening 18 and through the second opening 16 (similarto as shown in FIG. 2A). In yet further alternate embodiments, a firstend of the elastic member 60 and a second end of the elastic member 60can pass through the fourth opening 19 and through the second opening16. With the latter two options, the elastic member 60 can be kept togenerally one side of a rod member 80 inserted into the clamp 10.Accordingly, with the addition of the third opening 14 and the fourthopening 19, this advantageously provides a number of different optionsfor securing the clamp to bone.

The clamp 10 includes a unique set screw 25 having an extension member26 formed on a distal end thereof. As shown in FIG. 3A, the extensionmember 26 is a shaped protrusion that can extend through the bushing 28.When the elastic member 60 passes along the inner walls near the bushing28 (e.g., while entering or exiting the fourth opening 19), theextension member 26 of the set screw 25 is advantageously configured tocontact a portion of the elastic member 60 positioned therein. Thisadditional contact provided by the extension member 26 of the set screw25 helps to advantageously stabilize the elastic member 60 and, alongwith the bushing 28, helps to distribute the compressive load thatoccurs during downward threading of the screw 25. In some embodiments,the extension member 26 comprises a blunt tip to reduce the likelihoodof fraying of the elastic member 60.

FIGS. 4A-4D illustrate different views of an off-set clamp according tosome embodiments. The off-set clamp 100 is configured to receive anelastic member 60 (e.g., through slot or opening 116) on one side of theclamp 100, and a rod member 80 on an opposite side of the clamp 100. Theclamp 100 comprises an upper plate 110 having a first opening 114 and asecond opening 116 and a lower plate 120. The first opening 114 isconfigured to receive a set screw 125 that extends through the upperplate 110 and the lower plate 120. The second opening 116 is configuredto receive an elastic member 60 as discussed below.

As shown in FIG. 4B, the upper plate 110 can be physically separated andlifted away from the lower plate 120, thereby providing a space 130 forreceiving one or more portions of an elastic member 60 therethrough. Insome embodiments, the upper plate 110 can translate both vertically androtationally relative to the lower plate 120, thereby providing a largeenough space 130 (shown in FIG. 4B) for receiving an elastic member 60.The elastic member 60 can form a loop that extends around a bone member,with a first portion of the elastic member 60 in contact with a firstlower surface 121 of the lower plate 120 and a second portion of theelastic member 60 in contact with a second lower surface (not shown) onthe opposite side of the lower plate 120. The elastic member'strajectory is shown in FIGS. 4C and 4D. In some embodiments, the lowersurfaces 121 of the lower plate 120 can comprise an overhang forreceiving the elastic member 60 to prevent the elastic member fromsliding off of the assembly. With the portions of the elastic member 60in contact with the lower portions of the lower plate 120, first andsecond ends of the elastic member 60 can be inserted through the space130 (shown in FIG. 4B) created when the upper plate 110 is separatedfrom the lower plate 120. The first and second ends of the elasticmember 60 can then be inserted through the slot 116 formed in the upperplate 110.

With the elastic member 60 in place such that it is looped around a bonemember and such that both of its ends pass through the slot 116, theupper plate 110 can be brought downwardly onto the lower plate 120,thereby securing the elastic member 60 therein. To ensure that the upperplate 110 is secure to the lower plate 120, the set screw 125 can bedownwardly threaded, thereby compressively bringing the upper plate 110into a secure relationship with the lower plate 120. Advantageously, thedownward threading of the set screw 125 will also secure a rod member 80received in the rod opening 117 formed on the opposite ends of the clamp100. In other words, in some embodiments, the downward threading of theset screw 125 will both secure the elastic member 60 within the upperand lower plates on one side of the clamp 100, and simultaneously securean off-set rod member 80 that is positioned in a rod opening 117 on anopposite side of the clamp 100.

When the upper plate 110 is removed from the lower plate 120 (e.g.,vertically and/or rotationally) such that an elastic member 60 can bereceived in the space 130, the clamp 100 can be considered to be in an“open” or “unlocked” configuration. When the upper plate 110 isdownwardly secured to the lower plate 120 (e.g., via the set screw 125)such that the elastic member 60 is secured within the upper plate 110and the lower plate 120, the clamp 100 can be considered to be in a“closed” or “locked” configuration.

The off-set clamp 100 can be used as follows. When the clamp is ready toreceive the elastic member 60 and rod member 80, the upper plate 110 canbe raised and rotated slightly from the lower plate 120 to provide room(e.g., space 130) for inserting an elastic member (e.g., band) 60between the upper plate 110 and the lower plate 120. The elastic membercan wrap around a spinal portion (e.g., a lamina), and can extend alongthe outer, bottom side walls 121 of the lower plate 120. The bottom sidewalls 121 of the lower plate 120 can include an overhang to prevent theelastic member 60 from sliding off the clamp 100. Both ends of theelastic member 60 can continue to extend through the slot 116 formed inthe upper plate 110. On the opposite side of the clamp 100, a rod member80 can be received between the upper plate 110 and the lower plate 120.Before tightening the set screw 125 that extends between the upper plate110 and the lower plate 120, the rod member 80 is provisionally held inthe clamp 100 and is advantageously free to translate along itslongitudinal axis. With the elastic member 60 wrapped around a bonemember and the clamp 100, and the rod member 80 received on the oppositeend, the set screw 125 can be tightened such that the clamp 100 clampsdown on both the elastic member 60 and rod member 80. Thisadvantageously secures both the elastic member 60 between the upperplate 110 and lower plate 120 on one side of the clamp 100, and theoff-set rod member 80 within the rod opening 117 on the opposite side ofthe clamp 100.

FIGS. 5A and 5B illustrate different views of a tulip clamp according tosome embodiments. The tulip clamp 200 comprises a first arm 202 and anopposing second arm 204 that join at a base, thereby forming a U-shapedchannel for receiving a rod member 80. The first arm 202 comprises afirst angled slot or opening 214 for receiving a first end of an elasticmember 60 therethrough and the second arm 204 comprises a second angledslot or opening 216 for receiving a second end of the elastic member 60therethrough. The bottom of the elastic member 60 can form a loop thatpasses through a third opening 218 formed at the base of the tulipclamp. The loop is capable of looping around a bone member, such as alamina.

Advantageously, as shown in FIG. 5B, the third opening 218 of the tulipclamp 200 has slanted inner walls. These inner walls advantageouslyserve as a guide for first and second portions of the elastic member 60prior to the elastic member 60 opening into a loop below the clamp 200.In some embodiments, the third opening 218 has a width that is greaterthan a maximum width of the first opening 214 and/or the second opening216.

The tulip clamp 200 can be used as follows. An elastic member 60 canfirst be inserted through the tulip clamp 200 by passing first andsecond ends of the elastic member 60 through the base opening 218. Thefirst end of the elastic member 60 can pass through the angled slot oropening 214, while the second of the elastic member 60 can pass throughthe angled slot or opening 216. The bottom of the elastic member 60forms a loop that can be wrapped around a spinal portion, such as alamina. With the elastic member 60 in place, a rod member 80 can beintroduced into the U-shaped channel of the tulip head, such that theelastic member 60 contacts the rod member 80 on two sides. After the rodmember 80 is delivered downwardly into the tulip head, a locking capincluding a set screw (not shown) can be delivered onto the rod member80. In some embodiments, the locking cap can rest in locking cap slots231 found in the arms. In some embodiments, the set screw is threadedand interacts with threads on the arms of the tulip clamp. In otherembodiments, in lieu of a set screw and locking cap, a singlenon-threaded locking cap can be provided. Prior to locking the setscrew, the rod member 80 can be provisionally captured such that it isadvantageously free to move along its longitudinal axis. With theelastic member 60 and rod member 80 in place, a tensioner can tensionthe band to pull the spine up to the rod member 80 to correct adeformity. Once the deformity is corrected by tensioning the band, theset screw in the locking cap can be downwardly tightened to secure therod member 80 and elastic member 60 within the tulip clamp 200.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Moreover,the improved bone screw assemblies and related methods of use need notfeature all of the objects, advantages, features and aspects discussedabove. Thus, for example, those skilled in the art will recognize thatthe invention can be embodied or carried out in a manner that achievesor optimizes one advantage or a group of advantages as taught hereinwithout necessarily achieving other objects or advantages as may betaught or suggested herein. In addition, while a number of variations ofthe invention have been shown and described in detail, othermodifications and methods of use, which are within the scope of thisinvention, will be readily apparent to those of skill in the art basedupon this disclosure. It is contemplated that various combinations orsubcombinations of these specific features and aspects of embodimentsmay be made and still fall within the scope of the invention.Accordingly, it should be understood that various features and aspectsof the disclosed embodiments can be combined with or substituted for oneanother in order to form varying modes of the discussed bone screwassemblies. Thus, it is intended that the present invention cover themodifications and variations of this invention provided that they comewithin the scope of the appended claims or their equivalents.

What is claimed is:
 1. A spinal system comprising: a clamp for receivingan elongate rod therein, wherein the clamp comprises an inner openingfor receiving the elongate rod, a first opening in communication withthe inner opening, and a second opening in communication with the inneropening; a set screw received in the first opening of the clamp; abushing positioned at a distal end of the set screw; and an elasticmember received in the second opening of the clamp, wherein the elasticmember is configured to be in contact with the elongate rod received inthe clamp.
 2. The system of claim 1, wherein the inner opening is formedby an inner curved wall of the clamp.
 3. The system of claim 2, whereinthe inner curved wall of the clamp includes a groove for receiving theelastic member.
 4. The system of claim 1, wherein the set screw and thebushing are separate, removable pieces.
 5. The system of claim 1,wherein the set screw and the bushing are integrally formed.
 6. Thesystem of claim 1, wherein the bushing comprises a curved surface forcontacting the elastic member.
 7. The system of claim 1, wherein theelastic member comprises an elastic band.
 8. A spinal system comprising:a clamp for receiving an elongate rod therein, wherein the clampcomprises an inner opening for receiving the elongate rod, a firstopening in communication with the inner opening, and a second opening incommunication with the inner opening, wherein the inner opening includesa groove for receiving an elastic member therein; a set screw receivedin the first opening of the clamp; and an elastic member received in thesecond opening of the clamp, wherein the elastic member is configured tobe in contact with the elongate rod received in the clamp.
 9. The systemof claim 8, wherein the inner opening of the clamp downwardly faces theelongate rod such that the elongate rod is bottom-loaded into the clamp.10. The system of claim 8, wherein the clamp further comprises a thirdopening in communication with the inner opening.
 11. The system of claim10, wherein the elastic member extends through the second opening andthe third opening.
 12. The system of claim 8, wherein the system furthercomprises a bushing attached to a distal end of the set screw.
 13. Thesystem of claim 12, wherein the set screw includes an extension portionthat protrudes through a portion of the bushing.
 14. The system of claim8, wherein the elastic member comprises an elastic band having a widthof at least 4 mm.
 15. A spinal system comprising: a clamp for receivingan elongate rod therein, wherein the clamp comprises an inner openingfor receiving the elongate rod, a first opening in communication withthe inner opening, and a second opening in communication with the inneropening; a set screw received in the first opening of the clamp; abushing in contact with a distal end of the set screw, wherein the setscrew includes a protrusion that extends past a portion of the bushing;and an elastic member received in the second opening of the clamp,wherein the elastic member is configured to be in contact with theelongate rod received in the clamp.
 16. The system of claim 15, whereinthe bushing comprises a curved contact surface.
 17. The system of claim15, wherein the clamp further comprise a third opening for passing atleast a portion of the elastic member therethrough.
 18. The system ofclaim 15, wherein the clamp has a top plate and a bottom plate.
 19. Thesystem of claim 18, wherein the top plate is rotatable relative to thebottom plate.
 20. The system of claim 18, wherein the top plate can bemoved vertically relative to the bottom plate.